In the past, postoperative and post-trauma treatment of patients's joints commonly included immobilization. The affected joints were fixed by casts or traction for an extended duration. As a result of such immobilization various medical problems commonly arose. In particular, capsular, ligamentous and articular adhesions, thromboembolism, venos stasis, post-traumatic osteopenia, peripheral edema, muscle atrophy, and the like were commonly attributed to the immobilization.
It is now known that immobilization related medical problems could be reduced or eliminated by early mobilization of the affected joint. It has been found to be advantageous to initiate joint mobilization immediately following orthopedic surgery, in many instances in the operating and recovery rooms while the patient is still under anesthesia. Specifically, continuous passive motion of the affected joints has been found to be effective in reducing or eliminating the above-referenced medical problems, promoting faster healing, reducing the amount of pain and medications, improving the range of movement of the affected joint after recovery, and the like.
Continuous passive motion devices (CPMs) are typically motor driven and are designed to exercise a particular joint by repeatedly extending and flexing the joint. CPMs are capable of applying continuous motion to the joint in a repeatable, consistent manner and can be adjusted to operate at different speeds and within a defined range of motion. In such CPMs, it is important that the joint be anatomically aligned on the CPM. The limb is typically supported on a moveable carriage member which is driven by the motor. The carriage member includes a plate or other straps or padding (generally referred to as "softgoods") for directly receiving the human limb. Straps or the like are used to secure a portion of the limb to the plate or softgoods. For instance, in the case of a CPM for a leg, usually only the foot is strapped to the CPM while the remaining portion of the leg merely rests on the soft goods.
The problem with a CPM for the leg that is not anatomically correct is that it does not maintain consistent axial alignment with the patient's hip, knee, and ankle joints through the range of motion of the patient's limb. This is because the axes of the CPM and the axes of the patient's hip, knee, and ankle do not match. The machine shifts position and the axis points shift because the CPM uses a hinge located under the patient's thigh near the base of the buttocks. Accordingly, the pivot axis is not in alignment with the hip.
CPMs which receive limbs in an anatomically correct manner are known. For instance, CPMs for the knee joint typically receive the leg of the patient such that the pivot axes of the knee and hip joints are aligned with the pivot axes of the CPM. Such CPMs usually include a pair of carriage members for receiving the thigh and calf. The carriage members are pivotally connected to each other at one end. The other end of the carriage members are pivotally connected to a base. Since the pivot axis of the thigh hip joint is in the pelvic region, it is difficult to align the pivot axis of the thigh carriage member therewith.
Conventionally, this problem has been resolved by providing the base with a cantilevered bar which extends from the proximal end of the base toward the pelvic region. The distal end of the bar pivotally receives the carriage member for supporting the thigh. The bar can be mounted on either lateral side of the base to accommodate either the left leg or the right leg. While such CPMs achieve anatomical alignment, they are problematic in that the bar must be repositioned on the left or right side of the base to receive the limb to be exercised. That is, if the CPM was set up to exercise the right leg for a first patient and a second patient needed therapy for the left leg, the CPM would have to be dismounted and reassembled with the bar on the left lateral side of the base. This results in downtime between patients as well as creating unnecessary tasks for the therapists. Another problem is the cantilever effect places a great deal of stress on the CPM's proximal hinge. Yet, another problem is the overall length of existing anatomically correct CPMs. When the CPM aligns with the hip of the patient and the head of the hospital bed is raised, the mattress contacts the base of the hinge and pushes the CPM forward, trapping the CPM to the foot of the bed. Hence, a need has arisen for a bilateral CPM. That is, a CPM which can anatomically receive either a right limb or a left limb without the need to adjust the CPM in accordance with the particular limb to be rehabilitated.
Conventional CPMs are problematic in that the plate or softgoods for receiving the limb are rigidly secured to the carriage member and loosely receive the majority of the limb. That is, with respect to a leg, while a foot is strapped to the CPM, the thigh and calf rest loosely on the soft goods. Potentially, the patient could move or slip during the operation of the CPM and thereby cause the leg to move out of anatomical alignment with the CPM. As such, a need has developed for a CPM which securely receives the limb to prevent the same from moving out of anatomical alignment during the operation thereof.
Other CPMs have drawbacks in that they lack the requisite amount of power to raise and bend a relatively heavy limb. Many patients, such as a football player or perhaps a short nonflexible patient, can easily exceed the lifting capacity of conventional CPMs. Presently, this problem has been addressed by a machine which includes a large double reduction gear head that is supported by an external stand attached to the frame of a hospital bed. This machine exceeds seventy-five pounds in weight and is hard to move from patient to patient. Consequently, a need has arisen for a CPM which has the requisite power required to raise and bend a relatively heavy limb without increasing the overall size and weight of the CPM.
Conventional indirect drive CPMs drive one end of the carriage member at a substantially constant velocity. Because of the typical triangular configuration formed between the carriage member and base of the indirect drive CPMs, moving one end of the carriage member at a substantially constant velocity results in an varying angular velocity at the joint as it is repeatedly flexed and extended. Conventional CPMs are typically driven by electrically powered motors which have a speed that is directly proportional to the applied voltage and inversely proportional to the applied load. This usually results in speed variance that is inconsistent with patient comfort. Thus, a need has arisen for a CPM which can maintain constant angular velocity of the joint being treated.
The present invention overcomes many of the disadvantages inherent in the above-described CPMs by providing an anatomically correct CPM which is equally usable with both the right and left limbs thereof, thereby eliminating any downtime normally required to switch the CPM between right hand and left hand use. The present CPM is shorter than existing anatomically correct CPMs being approximately equal in length to non-anatomically correct CPMs. The present invention eliminates the need for a conventional thigh carriage and thus reduces the stress on the second hinge adjacent the patient's hip. The present invention flexes the joint at a constant angular velocity and is capable of lifting relatively heavy limbs. The present invention is also capable of achieving consistent anatomical alignment by firmly securing the limb to the CPM to prevent the patient's leg from shifting during therapy. Consequently, use of the present invention results in reduced downtime between patients, comfort to the patient, and enhanced rehabilitation of the joint.